This application claims the priority benefit under 35 U.S.C. § 119 of Japanese Patent Application No. 2005-378244 filed on Dec. 28, 2005, which is hereby incorporated in its entirety by reference.
1. Field
The presently disclosed subject matter relates to vehicle lights, and in particular, relates to a projector type vehicle light, such as a vehicle headlight provided in front of the vehicle body, a vehicle auxiliary headlight, a spot light, signal lights, a traffic light, and the like.
2. Description of Related Art
FIG. 1 is a cross sectional view of a conventional vehicle headlight. The vehicle headlight 1 shown in FIG. 1 includes a bulb 2 serving as a light source, a reflector 3, a projection lens 4, and a light-shading member 5.
The reflector 3 is composed of an elliptic surface having a first focus (rear focus) and a second focus (front focus), such that the bulb 2 is located in the vicinity of the first focus. The major axis thereof horizontally extends in the forward direction. The inside surface thereof serves as the reflecting surface. Examples of the elliptic reflecting surface include a revolved ellipsoid, an elliptic cylinder, a free curved surface based on an elliptic surface, and the like.
The projection lens 4 can include a convex lens having a rear focus (light source side) in the vicinity of the second focus of the reflector 3. The projection lens 4 is configured to converge the light received directly from the bulb 2 or light reflected by the reflector 3 to irradiate the converged light in the forward direction.
The light-shading member 5 is inserted in a light path to impart a desired light distribution pattern for passing-by type traveling (hereinafter, simply referred to as a “low beam” or “low beam distribution”) to the light irradiated in the forward direction. In reality, the light-shading member 5 is placed in the vicinity of the second focus of the reflector 3. The upper edge 5a thereof is formed into a desired form to shape the light distribution pattern with a cut-off line.
In the thus configured vehicle headlight 1, when the bulb 2 is energized, the light emitted therefrom travels directly in the forward direction or by being reflected by the reflector 3 to the vicinity of the second focus of the reflector 3. Thereafter, the light is converged by the projection lens 4 to be irradiated in the forward direction. At this time, part of the light passing in the vicinity of the light-shading member 5 is shaded by the member 5 to form a cut-off line by means of the upper edge 5a of the light-shading member 5. Accordingly, the light is irradiated as a low beam in the forward direction.
The formed cut-off line is projected by the projection lens 4 so as to form the cut-off line in the light distribution pattern in which the line extends from the center to the right slightly downward with respect to a horizontal line and from the center to the left side along the horizontal line in the case in which a headlight is used for a right-side traffic system. Therefore, the thus formed light distribution pattern extends on the lower side of the cut-off line. In other words, the light is irradiated so as to be suitable as a low beam.
In an actual case, the light distribution pattern is formed such that the light on the right side in the forward direction reaches relatively shorter distance and the light on the left side reaches relatively longer distance.
In the projector type vehicle headlight 1, the light-shading member 5 can be withdrawn from the light path to form another light distribution pattern for normal traveling (hereinafter referred to as a “high beam” or “high beam distribution”).
In the vehicle headlight 1 configured as described above, the low beam distribution pattern formed by the cut-off line is unchanged. In contrast to this, vehicle headlights having a controllable light distribution function which is commonly referred to as an adaptive front lighting system (AFS) have been commercially available recently. The AFS can direct the light distribution pattern of a headlight toward the traveling direction even when the vehicle travels along a curved road, thereby improving the visibility along the traveling direction. In addition to this, recent AFSs can provide a highway mode light distribution in which a distance visibility can be improved when traveling on a highway. An adverse weather mode light distribution can also be provided which is formed in consideration with visibility when traveling in the rain. An urban mode light distribution can be provided which is formed in consideration of preventing the dazzling of pedestrians when traveling on an urban road, and the like. These additional dedicated light distribution patterns have respective light distribution pattern specifications that are relatively newly introduced. In particular, the highway mode light distribution has an improved far distance visibility. To cope with this, the required luminous intensity for the low beam distribution in accordance with the light distribution specification therefor is increased from the upper limit of approximately 45,000 cd to approximately 80,000 cd. In addition to this, in some cases, the regulation for the angular position of the formed cut-off line is relaxed to some extent with respect to the conventional horizontally extending line.
One way to achieve certain features of the AFS as described above is via a vehicle headlight disclosed in Japanese Patent Laid-Open Publication No. 2004-327187 (corresponding to U.S. Patent Application Publication No. 2004/0213012). The vehicle headlight includes a first movable light-shading member configured to form a cut-off line for a low beam distribution, a second movable light-shading member shading the light irradiated on the road surface near the front of the vehicle body, and a leveling mechanism. The vehicle headlight can adjust the angular position of the cut-off line in the vertical direction by means of these components. In the vehicle headlight disclosed in these publications, the light-shading member forming the cut-off line for the low beam distribution is configured to adjust the cut-off angular position by 0.34 degrees upwards in order to reduce the shading amount of light. We ill now consider a case wherein a projection lens having a focus distance of, for example, approximately 40 mm is employed. In this case, the angular shift of the cut-off line by approximately 1 degree may correspond to 1 mm at the focus position of the projection lens. Therefore, in order to achieve the angular shift of the cut-off line by 0.34 degrees, it is necessary to precisely position the light-shading member by 0.34 mm, namely, in 1/100 mm order. This requires a complicated and accurately controllable movable structure for use as the light-shading member, resulting in increased manufacturing cost. In addition to this, mass production thereof is difficult due to the reliability and durability.
Now, a case will be considered wherein the conventional projector type vehicle headlight 1 can provide a highway mode light distribution which requires a far distance visibility. In this case, when the vehicle headlight 1 is provided with a vertical leveling mechanism to upwardly move the entire lamp unit, and the angular position of the cut-off line is shifted by 0.34 degrees, the maximum luminous intensity would be unchanged.
On the contrary, when the shaded light amount by the light-shading member is reduced to shift the angular cut-off position by an upward amount of 0.34 degrees, there is still a problem of positioning accuracy of the light-shading member. As a result, the obtained luminous intensity is increased only by 2,000 or 3,000 cd. Therefore, it is possible that enough far distance visibility cannot be attained, and a driver cannot clearly recognize the switching of modes from the normal mode light distribution to the highway mode light distribution.